Day of Defeat: Source is an online WWII first-person shooter constructed using the Half-Life 2 Source engine. You can play as one of many classes of troops, each with its own role and set of historically-accurate weapons. Day of Defeat: Source improves upon the original Day of Defeat by adding British troops, new models, visual effects, and an overhauled interface. You can also play through a set of new missions based on historical battles in the European theatre.